JPH0660802B2 - Interferometer and Fourier transform spectrometer including the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light source <radiation source>, a plurality of beam splitters <beam splitters> each of which functions in a different part of the light spectrum of the light source, and one light input beam from the light source. Light directing means for guiding through two beam splitters to generate two sub-beams
radiation directing means>, the two sub-beams reach different reflectors through separate optical paths,
An optical directing means which is returned to the beam splitter and is combined with the recombined beam;
Means for varying the difference in optical path length between two sub-beam optical paths <me
ans for varying the difference>, wherein the beam splitter is located at a fixed position and the light directing means directs the recombined beams from one selected beam splitter. It relates to an interferometer that has the ability to pass to one output. An example of a measuring instrument that uses such an interferometer is a Fourier transform spectrometer. The output signal of the detector that receives the recombined beam changes as a function of the changed optical path length, and this change can be analyzed by known Fourier transform methods to obtain the spectrum of the input light beam.

Such a spectrometer can be used in the infrared range, where the effective wavelength range is in particular 2.5 μ to 50 μ. The beam splitter actually used is provided on one plane of the optically flat light transmitting substrate, and in some cases, a compensator is provided on the head of this beam splitter. By virtue of the materials available for this beam splitter, light transmitting substrate and compensator, it is possible to obtain a single beam splitting assembly that is sufficiently transparent and has a beam splitting ratio of approximately 50/50 over the entire infrared region. Have difficulty. As such, at least two or more beam splitters are commonly used, each of which functions in a different portion of the infrared region. Therefore, it is necessary to provide means for moving the first beam splitter of the interferometer to replace it with the second beam splitter, in which case the parallel relationship between the plane of the second beam splitter and the plane of the first beam splitter becomes accurate. Care must be taken to do so. If this parallel relationship is lost, the center of the interference pattern at the detector will be displaced, resulting in a reduction in the quality of the signal obtained from the detector. For this reason, Fourier transform spectrometers that are effective over a wide spectral range have used a beam splitter turret with a precise mechanism to move each beam splitter of the interferometer sequentially to a position. Textbook "Advance in Raman Spectroscopy"
The Genzel interferometer described in Vol. 10, Chapter 5, Chapter 286-288, 1983 has the same number of six beam splitters mounted on the rim circumference of the wheel.

It is an object of the invention to provide a simple optical device using more than one beam splitter in an interferometer.

The interferometer of the present invention is such that the separated optical path of the sub-beam from the first beam splitter is parallel to the corresponding separated optical path of the sub-beam from the second beam splitter, and there are two pairs of correspondences. Each of the paired optical paths share a common mirror. This makes it possible to use the wide-range interferometer as a unit and improve the reproducibility of the operation when the beam splitter is attached to the fixed position of the interferometer. It allows each beam splitter to be adjusted separately when assembling the interferometer for each part of the spectrum, and these adjustments are not disturbed when changing the spectrum from one part to another. The light directing means further comprises means for individually generating a beam splitter, one for each of the beam splitters.

The light directing means includes a first fixed reflecting mirror on which the first recombined beam is incident, and a second movable reflecting mirror, and the second reflecting mirror is configured to emit the first recombined beam reflected from the first reflecting mirror. It is movable between a first position directed to the output side and a second position passing the second recombined beam to the output side.

Alternatively, the light directing means comprises a reflecting mirror unit, the reflecting mirror unit comprises a pair of plane parallel reflecting mirrors, the planes of the reflecting mirrors are spaced apart from each other, and the reflecting mirror unit is recombined into one. From a first position where the beam is reflected by each reflector of the reflector unit and exits the optical path to the detector,
The other recombined beam may be rotatable about an axis parallel to the plane of the reflector to a second position that passes directly along the optical path to the output side.

The means for producing a separate input beam may comprise means for directing a single input beam to a selected one of the beam splitters. This allows the use of a single input beam and collimating lens. Therefore, the input beam will only pass through one beam splitter at any one time period.

The light directing means includes an input reflecting element and a movable table that supports the output reflecting element, and the movable supporting table is attached to a sliding member so as to be movable to a plurality of positions, and at each of the plurality of positions. Arranging the input reflecting element so that light from the light source is effectively directed to the selected beam splitter, and arranging the output reflecting element so that the recombined beam is effectively directed to the output side from the selected beam splitter. You can

This also allows the use of a single input beam and collimating lens.

Therefore, the number of beam splitters can be increased without further complicating the light directing means, merely increasing the number of movements of the moving support that accommodates the additional beam splitters. In general, the optical path difference changing device in any type of interferometer is one of the expensive parts of the precision mechanism. Sharing the device between the two sub-beams from each beam splitter has the effect of simplifying the structure and making it worthwhile.

The first sub-beam from the beam splitter passes a certain optical path length before returning to the beam splitter, and the second sub-beam from the beam splitter passes through a common optical path length changing device before returning to the beam splitter. be able to. United States Patent No. 4,383,76
In the interferometer described in the specification No. 2, the optical path lengths of the two sub beams from the beam splitter are changed so that the optical path length of one sub beam increases and the optical path length of the other sub beam decreases accordingly. ing. The interferometer optical path length changer of the present invention can be smaller than the interferometers of the aforementioned U.S. Patents because it does not simultaneously accept two individual sub-beams from each beam splitter.

Embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, a broadband radiation source 1 directs the emitted light into two concave off-axis collimator reflectors 2 and 3.
And collimator mirrors 12 and
A parallel incident beam of 13 is supplied to beam splitters 4 and 5, respectively. The beam splitter 4 effectively functions in the long wavelength range, and the beam splitter 5 effectively functions in the short wavelength range, and the two wavelength ranges overlap to a small extent. Each beam splitter transforms its input beam into one sub-beam 14 (15) and the other sub-beam 16 (17).
Distribute to and. A beam-reversing plane reflecting mirror 6 common to the sub-beams 14 and 15 is provided within a constant optical path length. The other sub-beams 16 and 17 are incident on a common optical path length changing device which is mounted on a moving support 9 which rotates as an assembly about an axis 10 and which is a pair of flat and parallel reflectors 7. And 8 are included. This reflector 7
And 8 extend vertically enough to reflect both sub-beams 16 and 17 that have passed through the beam splitter. The flat beam inverting reflector 11 also has both sub-beams 16 and 17.
To extend vertically enough to reflect. The inverted sub-beam follows each optical path and returns to each beam splitter. First, the sub-beams 16 and 17 pass through the optical path length changing device to become the sub-beams 14 and 15, and then reach the respective beam splitters directly through the constant optical path length. Some of these sub-beams 14 and 15 pass through the beam splitter, and some of sub-beams 16 and 17 are reflected by the beam splitter and recombined beam 23.
And 24 are formed. The recombined beam is incident on a light directing device in the form of a switching arrangement comprising a fixed plane reflector 28 and a hinged plane reflector 26.

The lower recombination beam 24 travels straight to the detector 25 when the mirror 26 is lowered to position 27. The upper recombination beam 23 is reflected by the plane mirror 28 to the mirror 26. This reflector
When 26 is raised to the 45 ° position, the lower recombination beam 24 does not strike the detector and the upper recombination beam 23 strikes the detector. Enclose these optical components in a thermally stable enclosure
Hold in 38. The off-axis concave reflector 29 focuses the selected recombined beam on the detector 25 to produce an interference pattern on the concentric ring, which positions the detector at the center of the concentric ring. In use, the movable support 9 rotates in one direction, and in the middle of that, the reflecting mirror 26 is in one position, which is an angle that gives a desired optical path length. Then, the reflecting mirror 26 is moved to another position, and the movable support 9 is returned to its initial position again. The detector extracts the portion of the spectrum processed by each beam splitter during each rotation and analyzes its output.

An optical path length changing device is described in British Patent Application No. 8418308.

FIG. 2 shows the light directing means of FIG. 1 in more detail. The reflecting mirror 26 is rotatable about an axis 31 which is perpendicular to the plane of the drawing. At the position indicated by the solid line of the reflecting mirror 26, the direction of the switched beam is limited by an adjustable stop member 30 formed by screwing an adjusting screw into a fixing screw hole, and the ring pattern generated in the detector by the upper beam is adjusted. Adjust to the center. In the position below the dotted line, the reflector 26 drops below the optical path of the beam 24, which makes it
As a beam, the beam 23 is absorbed by an instrument container (not shown). If this switching arrangement is used in an interferometer that is part of a Fourier Transform spectrometer, the position of the reflector 26 will be stable during scanning of the interferogram, as will be explained later with reference to FIG. It is only necessary to have an exact reproducible position.

In FIG. 3, centering on an axis 33 perpendicular to the plane of the drawing,
7 shows another switching arrangement utilizing a rotatable mirror mount 32. Two flat reflectors 34 and 35 are rigidly fixed to the mount 32 with their reflective surfaces facing each other and parallel to each other and parallel to the axis 33. This mounting table 32
In the solid line position of the beam, the beam 23 is reflected once by the reflecting mirrors 34 and 36, respectively, and the beam 35 parallel to the original beam direction is irrespective of the angular position of the mounting table 32 on which both reflecting mirrors on which the beams are incident are fixed. Becomes Due to the parallel relationship of the switched beam 23 with respect to its original beam direction, a wide tolerance in the switched position of the mount 32 is guaranteed. The effect of the change in the switching position of the mounting table is shown in Fig. 37 for the switching beam.
As shown in, it is laterally parallel to itself. Since the ring-shaped interference fringes are focused and generated by the concave reflecting mirror 29, the center position of the ring-shaped interference fringes is not affected by this lateral shift.

The switching arrangements of FIGS. 2 and 3 show means for switching the recombined beams of two interferometers to one detector. This will be apparent to one of ordinary skill in the art by combining two or more interferometers with the interlocking switches of FIGS. 2 or 3 to select one recombined beam for the detector.

Although the Michelson interferometer has been described with respect to FIG. 1, it should be understood that other known interferometers that produce parallel recombination beams can be used. Further, the means for changing the optical path length of one arm of each interferometer rotates as an assembly.
The use of a pair of flat parallel mirrors has been described. In addition, other known methods of changing the optical path length can be used in the interferometer.

For more information on interferometers and other optical path length changers, see Chapter 8 of "The Design of Optical Spectrometer" by J. F. James and R. S. Sternberg, published in 1969 by Chapman & Hall. Please refer to. US Pat. No. 4,387,362 describes several optical path length changing devices that can be used in the present invention.

The following is described for use in the Fourier transform interferometer operating in the infrared region of the present invention. In this infrared region, the individual beam splitters have their anti-longevity range limited due to the available materials, and the design of the filter coating that provides 50% transmission and 50% reflection. Effective wavelength range, for example, to utilize 4000cm ^-1 ~2000cm ^-1, it is necessary to pair the beamsplitter covers the parts of this wavelength range.

FIG. 4 shows a Fourier transform interferometer according to the present invention. The optics of the interferometer are positioned and supported in relative positions by a structure 39, which is generally box-shaped and has an inner wall. The input beams 12 and 13 are provided by a broadband infrared source 1 and are collimated by concave reflectors 2 and 3, respectively, and the rest of the double interferometer is as described with reference to FIG.

The flat reflectors 6 and 11 of the interferometer of FIG. 1 are mounted on a tilt angle adjustment device as described in pending UK patent application No. 8416263. One of these adjusting devices tilts the reflected beam in one plane and another adjusting device tilts the beam in the other plane. When the device is assembled during manufacture, the adjustment device is used to bring the recombined beam 35 into the detector 25 to center the stripes. Therefore, these adjustment devices are fixed in position with respect to the structure in the stress-free state described in the above-mentioned copending application.

The movable support base 1 is rotated by a motor 102 mounted at a position apart from the support structure. An auxiliary beam 106 of visible radiation, for example a helium neon laser 90, is fed through one optical path of the interferometer to a recombination beam 93 to a separate detector 94.
To form interference fringes. The output of this detector is used in the waveform shaping circuit 96 to generate a sampling instantaneous signal generated at intervals of one wavelength, or the laser light source is divided into small parts to change the optical path length. These sampling signals control sampling instants, and by this control, the output of the detector 25 is sampled at each instant and the computer
Beam 97 using a program based on the well-known Cooley-Toukey algorithm.
Calculate the spectrum 98 of. In addition, the speed of the motor 102 that drives the movable support table is controlled by the control circuit 101 that responds to the sampling instantaneous signal to keep the sampling speed constant.

The selectively coupled beam 35 exiting the switching arrangement is passed through a sample 95 of material and the absorbance is measured as a function of wavelength. The concave condensing reflecting mirror 29 is schematically shown as a lens element.

In an actual interferometer, the lower interferometer in FIG.
It can be used for the short wavelength range of 2.5 μ to 25 μ. The reason is that the position of the optics becomes more critical at shorter wavelengths and the combined beam of this interferometer passes directly through the reflector 29. An upper switched interferometer, for example
Used in the long wavelength range of 25μ to 50μ.

As a manufacturing step, the lower interferometer is first assembled using the fixed beam inverting mirrors 6 and 11 to center the beam at the center of the fringe pattern at the detector. For this task, a visible laser stripe pattern can be used, which is then used to find the center of the white light stripe pattern, which has an optical path length of two arms of platform 9. Only visible if they are equalized by rotation. The infrared source is then used to make the final adjustments to reflectors 6 and 11 to maximize the detector output.

The upper combined beam is then selected using the switching arrangement and the upper beam splitter 4 and the reflector stop member 30 are selected.
Is adjusted so that the output of the detector 25 becomes maximum and the long wavelength fringe pattern of the detector is centered.

A beam switching arrangement as shown in FIG. 2 or 3 is used to provide the two input beams 12 and 13 to the other input side of the two interferometers shown in FIG. Flat reflector 42 with fixed input beam 43 using a single concave collimator reflector 3 and hinged flat reflector
Supply switching arrangement comprising 40. When the mirror 40 is lowered to position 41, the input beam 43 is
It passes directly to the lower beam splitter 5 as shown by. When the hinged reflector 40 is positioned upward at an angle of 45 °, the input beam 43 passes through the reflector 42 and reaches the upper beam splitter 4. The movements of the reflectors 40 and 26 are interlocked, either they are both underside or they are hinged together and are above, and the light is either the upper interferometer or the lower interferometer. Whichever of

FIG. 6 shows another example of the present invention, in which parts corresponding to those in FIGS. 1 and 5 are designated by the same reference numerals. The light directing means comprises an L-shaped carriage 50 which is slidable in the direction of arrow 51 along a fixed vertical column 52 having a square cross section, which carriage 50 is only 1 in the direction of arrow 51. Have freedom. The sub-beams 14 and 16 and the recombination beam 23 are perpendicular to the arrow direction 51. By carriage 50, parallel to beams 14 and 23, 45 in the direction of arrow 51
It supports an input reflecting element in the form of a flat reflector 53 which is tilted by °. The light source 1 produces vertically downward, parallel input beams parallel to the arrow direction 51, which are reflected horizontally towards a number of beam splitters 4, 5 and 55 which are aligned upwards in the direction of the arrow direction 51. To be done. The carriage 50 further supports an output reflecting element in the form of a plane reflector 56 parallel to the beams 12 and 16 and inclined in the direction of arrow 51 and 45 ° to reflect the recombination beam 23 vertically downwards for clarity. Therefore, the light is incident on the detector 25 through the focusing means which is omitted. Also, the input and output reflective elements can be prisms. In the lower position 57 of the carriage, shown in phantom in the figure, the input beam 13 is parallel to, but below, the beam 12 in the upper position and therefore impinges on the beam splitter 5. The recombination beam 24 is located below the recombination beam 23 in the upper position, but with a lower reflector 56.
After being reflected by, the light enters the detector along the first optical path 35. Furthermore, the beam splitter 55 can be selected when the carriage moves upward. You can also stack multiple beam splitters,
The number of beam splitters at this time is limited by the beam diameter and the maximum actual heights of the plane reflecting mirrors 6 and 11 for reflecting the sub-beams and the parallel reflecting mirrors 7 and 8 including the optical path length changing device.

Sliding movement of carriage 50 increases the distance from light source 1 to reflector 53, and at the same time reduces the distance from detector 25 to reflector 56 by the same amount, and vice versa. Is. Therefore, the optical path length between the light source and the detector remains constant even if the beam splitter is changed. This has the advantage that the imaging from the light source to the detector is constant. The light source has a finite size, but the input beam is almost parallel after passing through the collimator lens. Therefore, the beam width at the detector lens is constant in this arrangement. This allows the detector lens to be minimally sized to receive the entire recombined beam from any beam splitter.

[Brief description of drawings]

FIG. 1 is a diagrammatic external view showing a double interferometer of the present invention, FIG. 2 is a diagram showing a first output beam switching arrangement, and FIG. 3 is a line showing a second output beam switching arrangement. FIG. 4 is a diagram showing a Fourier transform infrared spectrometer using the double interferometer of FIG. 1, FIG. 5 is a diagram showing another example of the double interferometer, and FIG. 6 is FIG. 3 is a diagram showing a multiple interferometer. 1 ...... Broadband light source 2, 3 ...... Collimator reflector 4,5 ...... Beam splitter 6 ...... Beam reversing reflector 7, 8 …… Parallel plane reflector 9 …… Moving support 10 …… Axis 11 …… Beam Inverting mirror 12, 13 …… Input beam 14 to 17 …… Sub-beam 23, 24 …… Recombination beam 25 …… Detector 26 …… Hinge-stop plane reflector 28 …… Fixed plane reflector 38 …… Enclosure

Claims (17)

[Claims] 1. A light source, a plurality of beam splitters, each of which functions in a different part of the light spectrum of the light source, and one light input beam guided from the light source through one beam splitter and two sub-beams. A light directing means for producing the light, wherein the two sub-beams travel through separate optical paths to different reflectors and back to the beam splitter to be combined into a recombined beam. An interferometer comprising: a directing means and a means for varying an optical path length difference between two sub-beam optical paths, wherein the beam splitter is located at a fixed position, and the optical directing means is the recombining means. In an interferometer capable of passing a selected beam from one selected beam splitter to one output, the first beam splitter Said separated optical path of these sub-beams being parallel to the corresponding separated optical path of the sub-beam from the second beam splitter,
And an interferometer characterized in that each of the two corresponding pairs of optical paths share a common mirror (6,11). 2. The interferometer according to claim 1, wherein said light directing means further comprises means for generating a separate input beam, one for each beam splitter. 3. The light directing means comprises a first fixed reflecting mirror on which a first recombined beam is incident and a second movable reflecting mirror,
The second reflecting mirror is movable between a first position where the first recombining beam reflected from the first reflecting mirror is directed to the output side and a second position where the second recombining beam is passed to the output side. Claims 1 or 2 characterized in that
The interferometer described in the item. 4. The light directing means comprises a reflecting mirror unit, the reflecting mirror unit comprising a pair of plane parallel reflecting mirrors, the planes of the reflecting mirrors being spaced apart from each other, and the reflecting mirror unit comprising: From a first position where one recombined beam is reflected by each reflector of the reflector unit and exits the optical path to the detector, the other recombined beam passes directly along the optical path to the output side. The interferometer according to claim 1 or 2, wherein the interferometer is rotatable about an axis parallel to the plane of the reflecting mirror. 5. Interference according to claim 2, characterized in that the means for generating the individual input beams comprise means for directing a single input beam to a selected one of the beam splitters. Total. 6. The light directing means comprises an input reflection element and a movable base for supporting the output reflection element, and the movable support base is mounted on a sliding member so as to be movable to a plurality of positions. The input reflection element is arranged so that the light from the light source is effectively directed to the selected beam splitter at each position of
The interferometer according to claim 1, wherein the output reflection element is arranged so that the recombined beam is effectively directed to the output side from the selected beam splitter. 7. The movable support base is slidable in a direction parallel to the plane of the beam splitter, and the input and output reflection elements are arranged at an angle of 45 ° with respect to the moving direction of the movable support base. 7. The interferometer according to claim 6, wherein the reflected and recombined beam extends parallel to the moving direction of the moving support. 8. The sub-beams from each beam splitter share a common means for varying the difference in optical path length, according to any one of claims 1 to 7. Interferometer described. 9. The first sub-beam from the beam splitter passes a certain optical path length before returning to the beam splitter, and the second sub-beam from the beam splitter passes through a common optical path length varying device before returning to the beam splitter. The interferometer according to claim 8, wherein the interferometer is configured to pass through an optical path. 10. The common optical path length varying device comprises a plurality of planar reflectors rigidly and interconnected to form an assembly, and a second sub-beam to a first reflector of the reflector assembly. Means for directing, wherein the plurality of planar reflectors are suitably mounted such that they are parallel to the direction in which the second sub-beam passes through this assembly by reflection from each of the plurality of reflectors and is incident on the first reflector of the assembly. And exiting the assembly in the same direction, and the optical path length varying device rotates the assembly about the axis to change the angle of incidence of the second sub-beam on the reflector, thereby causing the optical path of the second sub-beam to change. 10. The interferometer according to claim 9, further comprising means for changing the optical path length. 11. A beam inverting flat reflecting mirror is provided in the optical path at a right angle to the outgoing direction of the second sub-beam so that the outgoing second sub-beam passes through the optical path reaching the beam splitter via the reflecting mirror assembly. The interferometer according to claim 10, characterized in that. 12. The reflector assembly comprises a pair of parallel plane reflectors, the planes of the reflectors being spaced apart from each other, the reflectors extending parallel to the axis of rotation, and all of the second sub-beams. The interferometer according to claim 10 or 11, wherein the interferometer is configured to receive light. 13. The interferometer according to claim 12, wherein the rotation axis is made substantially parallel to the reflecting mirror surfaces of the pair of flat reflecting mirrors. 14. The input beams are parallel to each other, the sub-beams are parallel to each other, and the recombined beams are parallel to each other, and a first beam-reflecting common-plane mirror is provided for the first sub-beams. 14. The interferometer according to claim 13, wherein the interferometer is arranged, and the second beam inverting common reflecting mirror is arranged for the second beam. 15. An interferometer as claimed in any one of claims 1 to 14, characterized in that means are provided for focusing the selected recombined beam on a detector. 16. A light source and a plurality of beam splitters, each of which functions in a different portion of the light spectrum of the light source.
A light directing means for directing one light input beam from a light source through one beam splitter to generate two sub-beams, the two sub-beams passing through separate optical paths to different reflectors. An interferometer comprising a light directing means that reaches the beam splitter, returns to the beam splitter and is combined with the recombined beam, and means for varying the difference in optical path length between the two sub-beam optical paths. Thus, in a Fourier transform spectrometer including an interferometer, the beam splitter being located at a fixed location and the light directing means being capable of passing the recombined beams from one selected beam splitter to one output. , The separated beam path of the sub-beam from the first beam splitter is a pair of sub-beams from the second beam splitter. Parallel to the corresponding separated optical paths, each of the two pairs of corresponding optical paths share a common mirror (6,11), and the Fourier transform spectrometer comprises a detector output signal , A Fourier transform spectrometer, having means for processing as a function of the variation of the optical path difference of the selected sub-beams and providing the spectrum of the light. 17. The Fourier transform spectroscopy according to claim 16, wherein the interferometer is mounted in a support suspended inside a thermally insulated frame. Total. "